Recently, a thin tape is used in a tape cartridge of video tape and the like comprising a parallel-two-reel system for enabling long recording. However, when a thin tape having a thickness of 15 .mu.m or less is forwarded and rewound at high speed, air layers are formed between each tape layer wound around reels. As a result, the tape slips in its widthwise direction (which is perpendicular to the tape moving direction). When the tape slips in its widthwise direction, the edges of the tape rub the bottom or ceiling of the housing of the tape cartridge, and the edges of the tape are damaged. Additionally, when the tape protrudes from the reels in its widthwise direction, the load for drawing the tape out from the tape cartridge becomes very heavy.
When dust which is created by rubbing the edges of the tape on the bottom or ceiling of the housing or which is naturally present in the air adheres on a recording face of the tape, the dust leads to recording and replaying signal failures. In particular, the tape is affected more by the adhered dust as the recording density becomes higher. Accordingly, the rate of error occurrence worsens enormously when the tape is repeatedly forwarded and rewound, and the number of drop-outs also increases.
An example of the tape cartridge containing the thin tape and used for high-density recording and reproducing is disclosed in U.S. Pat. No. 3,692,255. Another example is disclosed in U.S. Pat. No. 5,081,555.
First, the conventional tape cartridge disclosed in U.S. Pat. No. 3,692,255 is described referring to FIG. 13. This Patent relates to a tape cartridge in which reels are freely pivoted without engaging any driving mechanism and a tape is moved by a belt driving mechanism. As shown in FIG. 13, a cartridge 101 is comprised of a thin box-shaped top cover 103 made of resin and a base plate 102 made of a metal such as an aluminum plate. Top cover 103 is fixed on base plate 102 by screws. On a bottom face of base plate 102, a pair of reels 104 are freely and rotatively pivoted. A magnetic tape 105 is wound around between reels 104. Tape 105 is guided along a front face wall 103b in the inside by a pair of tape guides 106 disposed on base plate 102. Furthermore, a belt driving roller 107 is rotatively pivoted on the front side in the center of base plate 102. Also, a pair of belt guiding rollers 108 which are rotatively pivoted at both ends on the rear side of base plate 102. A belt 109 having elasticity is guided by belt driving roller 107 and both belt guiding rollers 108. Belt 109 is formed substantially in a kind of T form with strong tension of 1.6 N or higher. A part of belt 109 contacts and presses the outer circumference of both parts 105a of tape 105 which are respectively wound around both reels 104.
When tape cartridge 101 is loaded in a recording-reproducing apparatus (not shown in the figure), a door 111, which is rotatively pivoted between base plate 102 and top cover 103, is rotated in the direction shown by arrow A in the figure such that door 111 is to be in a position shown by one dotted chain line in the figure. Thus, a cutout part 110 which is formed at one end on the front side of base plate 102 and top cover 103 is opened. Subsequently, a magnetic head 112 provided on the recording-reproducing apparatus is inserted into cutout part 110, and magnetic head 112 contacts the recording face of tape 105. At the same time, a driving roller 113 provided on the recording-reproducing apparatus is inserted into an opening part 114 which formed on top cover 103, and driving roller 113 presses and rotates an outer circumference of a a part 107b having a larger diameter and integrally formed with and on top of a belt winding face 107a of belt driving roller 107. Then, belt driving roller 107 is rotatively driven by the rotation of driving roller 113, for example, in the direction shown by arrow B in the figure. Thus, belt 109 is driven in the direction shown by arrow C. Due to the movement of belt 109, the part 105a of tape 105 wound around both reels 104 are rotatively driven in the direction shown by arrow D in the figure. Accordingly, tape 105 moves in the direction shown by arrow E in the figure at a relatively high speed of 25 to 120 inch per second. At this time, recording and reproducing are performed by a magnetic head 112 onto the recording face of tape 105.
Next, the conventional tape cartridge disclosed in U.S. Pat. No. 5,081,555 is described referring to FIG. 14 and FIG. 15. This Patent relates to a compact cassette used mainly for music, and has an object of removing dust adhered on a recording face of a magnetic tape. As shown in FIG. 14 or 15, a pair of reels 204a, 204b are rotatively pivoted on a bottom face of a base member 202, and a magnetic tape 205 is wound around between both reels 204a, 204b. Tape 205 is guided by a pair of tape guides 206 disposed on base member 202 and is passed along an opening part 202a in the inside. Furthermore, a ring-shaped or substantially V-letter-shaped flexible strip 207 is provided in the center part of base member 202. Outer faces of flexible strip 207 are respectively in contact with a recording face of parts 205a, 205b of tape 205 wound around both reels 204a, 204b. Flexible strip 207 is formed, for example, of elastic materials such as polytetrafluoroethylene (PTFE). On the surfaces of flexible strip 207 contacting the recording face of tape 205, a non-woven fabric or paper and the like is formed as a cleaning layer.
In general, both of the tape cartridges 101 and 201 described above are configured such that the recording faces of tapes 105 and 205 are respectively pressed by belt 109 and flexible strip 207 while the tape moves. Therefore, it is considered as possible to wind tapes 105 and 205 on reels 104 and 204a, 204b while eliminating the air from gaps between the tape layers. In this case, even if the tape is forwarded at a relatively high speed, tape 105 or 205 does not slip out in the widthwise direction, so as to wind the tape in a stable condition. Furthermore, the dust adhered on the tape is scratched off by belt 109 or flexible strip 207, so that the rate of error occurrence or the occurrence of drop-outs can be reduced.
In order to attain a high-density recording, it is necessary to record and reproduce relatively high-frequency signals with high density. Therefore, a rotary-head system is generally used in which a tape is drawn out from a cartridge and is wound around a rotary-head drum for recording and reproducing. However, since the tape is driven by the belt in the tape cartridge according to U.S. Pat. No. 3,692,255, the friction coefficient between the tape and the belt is high, and in addition, the load due to tension of the belt is also high. As a result, when the tape cartridge 101 is used, a large drawing torque is needed to draw tape 105 out from tape cartridge 101. Thus, the problem with this type is that tape cartridge 101 can not be used for a recording-reproducing apparatus comprising a general rotary head system employed in a video taperecorder or in computer data storage. Also, especially when a thin tape (which dislikes the air layers formed between tapes) is used, when they are taken up on reels, the tape tended to lengthen or be cut off when it was attempted forcibly to draw out the tape against the load.
On the other hand, when the tape cartridge 201 according to U.S. Pat. No. 5,081,555 is used, flexible strip 207 is indeed formed of resin materials such as PTFE, but these materials do not possess the ability to expand and contract, despite being elastic. In other words, the ring-shaped flexible strip 207 does not expand in its full circumference, but remains constant. Therefore, when the tape parts which were wound around reels 204 change their diameters, flexible strip 207 slightly deforms itself responding to these changes, but the deformation is not so great as to cause expansion. As the tape travels, the diameter of the part 205a of tape 205 wound around one reel 204a becomes gradually larger, while the diameter of the other part 205b of tape 205 wound around the other reel 204b becomes smaller, so that flexible strip 207 is considered to traverse between these two reels 204a, 204b.
Since tape 205 travels at a constant speed, when the diameter of the part 205b of tape 205 wound around reel 204b is small, the curvature of the part 205b changes largely. Therefore, since flexible strip 207 can not move and deform itself responding to the changes in diameter of the parts 205a, 205b of tape 205 wound around reels 204a, 204b, it may also happen that flexible strip 207 can not contact the surface of parts 205a, 205b of tape 205 wound around reels 204a, 204b. As a result, air which is present between each tape layer of parts 205a, 205b of tape 205 can not be eliminated, so that the tape 205 slips out in the width direction, which leads to the problem that the tape can not be wound around reels 204a, 204b in a stable condition. Furthermore, the dust adhered on the recording face of tape 205 can not be scratched off, so it was difficult to reduce rate of error occurrence or drop-outs and the like.
Meanwhile, one of the performance characteristics required for a magnetic tape which is used repeatedly for recording and reproducing is a still-life. The still-life indicates durability of a tape when the tape loaded in a rotary head is reproduced while stopped for the purpose of outputting a still picture image in a video taperecorder and the like. The still-life plays a particularly important part in a broadcasting station which conducts video editorial operations, during which the still-life needs to stand for many hours. Also, in case of a domestic video taperecorder or a recording-reproducing apparatus for music use and the like, this system of pausing the moving tape in the loaded condition is used widely for improving quick access. Therefore, the still-life is also extremely important in the field of home electrical devices.
In order to improve the still-life, a lubricant such as fatty acid etc. has been applied on a magnetic layer in the past, so that the lubricity between the magnetic layer of a tape and the magnetic head improves. The more a lubricant is added, the better the lubricity of the applied film with the magnetic head. However, the strength of the applied film is greatly influenced by the amount at lubricant. If too much lubricant is added, the strength of the applied film conversely deteriorates, so that a predetermined still-life can not be secured. To prevent this kind of deterioration in the strength of the applied film from occurring, it is also possible to employ a method of applying a lubricant after forming a magnetic layer of the tape. However, the lubricant must be applied by dissolving it in an organic solvent and the like. In this case, the magnetic layer is eroded by the organic solvent, which leads to deterioration of the applied film, so that a satisfactory still-life can not be attained.
Furthermore, since the positions of reel stands in a recording-reproducing apparatus differ in each case, reels of the tape cartridge comprising a parallel-two-reel system are not fixed to the cartridge. Instead, there is enough tolerance provided to facilitate engagement of the reels with the reel stands. As a result, the reels move with great acceleration due to vibrations caused during transportation or shock etc. when cartridges are accidentally dropped, and the tape (particularly the tape that is wound around with a large volume of tape) is drawn suddenly, it causes damages to the tape. This phenomenon is especially notable for thin tapes. In addition, the vibrations during transportation etc. cause tapes to become loose which then show loading failures when loaded.